Lake Rotorua

Lake Rotorua

Lake Rotorua

"Lake in a basin".  A number of the Rotorua lakes were named by Ihenga, a grandson of the captain of the Arawa canoe Tamatekapua.

 He named the largest lake, Rotorua nui ā Kahu-matamomoe, in honour of his father-in-law and uncle, Kahumatamomoe. "Rotorua nui" refers to the large basin-like lake.  

Lake Rotorua is the largest lake in the district and the most productive trout fishery in New Zealand. With the city of Rotorua on its shores, it is much valued and used by locals and tourists alike.

It is probably New Zealand's best-known lake island, and is closely associated with one of the best-known Māori legends, that of Hinemoa and Tutanekai. It is said that Hinemoa swam across the lake to her lover Tutanekai who lived on Mokoia Island.

The lake was formed from the crater of a large volcano in the Taupo Volcanic Zone.  The quality of the water in Lake Rotorua also affects Lake Rotoiti as the two lakes are linked by the Ohau Channel.

Water quality status

Great achievements have been made for Lake Rotorua and the water quality continues to be the best it has been in decades.  The lake remains at or around its target Trophic Level Index (TLI) of 4.2depending on the climatic conditions. Regional Council doses aluminium sulphate into two streams which flow to the lake, the Puarenga and Utuhina, the aluminium sulphate locks the phosphorous into the sediment removing it from the water column. This intervention is a key reason why the lake is achieving its water quality target but this is not a long term solution for the lake.

The key to long term sustainable water quality will be reducing nutrients from land-use.  A Stakeholder Advisory Group was formed with representatives from the pastoral, water quality, forestry and iwi sectors.  This collaborative forum was integral to the development of an integrated framework made up of solutions for reducing nitrogen that enters the lake, including the development of Plan Change 10.

 

Solution for long term water quality

An integrated framework of solutions aims to achieve long term water quality. It includes:

  • Proposed Plan Change 10 – a set of rules to remove 140 tonne of nitrogen from entering Lake Rotorua from pastoral farming.
  • Gorse Conversion Programme - $2.5 million fund to remove 30 tonnes of nitrogen from entering Lake Rotorua
  • Lake Rotorua Incentives Programme - $40 million incentive fund to remove 100 tonnes of nitrogen from entering Lake Rotorua through voluntary land use/management change
  • Engineering solutions – Bay of Plenty Regional Council will use engineering initiatives to remove 50 tonnes of nitrogen from entering Lake Rotorua

 

At a glance

 

Lake size:

8060 ha

Catchment area

50060 ha

Elevation

280 m

Average depth:

11 m

Deepest point: 

45 m

Formed:

140,000 years ago

Has geothermal input

 

 

 

 

 

 

 

 

 

 

 

 

Catchment Map

Click here to view image of map.

 

Groundwater Information

  Area (ha)
Groundwater catchment 53,789
Groundwater catchment (not including Lake Rotorua) 45,704

 

 

 

 

Land Slope

Slope (degrees) Area (ha)
0-7.9 18,109
8-15.9 9,672
16-25.9 7,652
26+ 6,178
No slope information 398

 

 

 

 

 

 

Rainfall

100mm rainfall bands (mean precipitation 1981-2010)  
1300-1400mm 692
1400-1500mm 2,231
1500-1600mm 9,567
1600-1700mm 5,271
1700-1800mm 5,908
1800-1900mm 4,710
1900-2000mm 2,830
2000-2100mm 2,761
2100-2200mm 2,946
2200-2300mm 2,267
2300-2400mm 2,826

 

 

 

 

 

 

 

 

 

Land Use Capability Class (LUC)

Land Use Class Area (ha)
2 534
3 5,227
4 13,148
6 17,421
7 4,363
8 843
Town or Lake 473
   

 

 

 

 

 

 

 

Target and Results

To meet community expectations Lake Rotorua needs to reach a sustainable load of 435 tonnes of nitrogen and managephosphorous entering the lake.  We also need to reduce the impact of nutrients already in the lake. 

Water Quality target

4.2 

2014 result

4.2

2015 result

4.4

2016 Result

4.4.

 

 

 

 

 

 

Nutrient research

Report title Author/s Summary Date
Management of Phosphorous and nitrogen inputs to Lake Rotorua, New Zealand J.C. Rutherford, R.D. Pridmore and E. White This is the original report that informed that a sustainable load of 435 tonnes of N and a reduction of 10 tonnes of phosphorus is required to meet water quality targets (pre-1960s) 1989

 

Actions and achievements

Action

Achieved as at June 2016

Status

Land use and land management change (not Incentives Scheme)

3.94T N

.08 T P

 

Sewerage Reticulation

9.74 T N

2.5.86 T P

Lakeside communities in Brunswick, Hinemoa Point, Tarawera Road and Paradise Valley have connected to sewerage reticulation.

Tikitere Geothermal Treatment

0

Plant scheduled for construction 2018-2019.

Floating wetland

0.07 T N
0.02 T P

Floating wetland established.

Detainment bunds

0.02 T P

8 detainment bunds have been installed 

Action Plan

Lake Action Plans direct what steps need to be taken to improve lake water quality to meet the communitys' expectations

Read Lake Rotorua & Rotoiti Action Plan